Theft prevention system



Dec. 16, 1969 w. D.' CLINE l 3,484,775

' THEFT PREVENTION SYSTEM Filed oct. 20, 1965 2 Sheets-Sheet l Dec. 16,1969 w. D. CLINE 3,484,775

THEFT PREVENTION SYSTEM Filed Oct. 20, 1965 2 Sheets-Sheet 2 I 54T I I7a Pad/er I United States Patent O 3,484,775 THEFT PREVENTION SYSTEMWallace Dean Cline, P.O. Box A-6829, Represa, Calif. 95671 Filed Oct.20, 1965, Ser. No. 498,457 Int. Cl. G08b 21/00, 17/06, 25/00 U.S. Cl.340-280 3 Claims ABSTRACT F THE DISCLOSURE A theft prevention alarmcircuit for appliances is located in a boxwhich is plugged into astandard wall socket, and a standard appliance plug is plugged into thebox. Provision is made so that the alarm box s not easily unplugged, andwhen the appliance plug is removed from the box an alarm is given.

sets in hotel and motel rooms. A recent survey revealed that motelsthroughout the United States were losing an average of eight percent(8%) of their television installations each year. To avoid this problem,some motel owners have rigidly secured their television sets into heavypieces of furniture. These arrangements are expensive and frequentlyimpair ilexibility in viewing the television set from the desiredlocation. In other cases, permanent wiring installations have beeneffected at substantial cost.

The principal object of the present invention is to prevent the theft oftelevision sets or other appliances by the use of an inexpensive warningapparatus which does not require professional installation.

In accordance with an illustrative embodiment of the invention, a smallbox may be plugged into an ordinary electrical outlet, and thetelevision Set may be plugged in to the box. Suitable arrangements areprovided for preventing removal of the box from the wall socket, atleast while the television set is plugged in. The television plug,however, may be removed from the box, energizing an alarm circuit by aswitching mechanism within the box.

In a preferred embodiment of the invention, the box may contain anoscillator which is normally de-energized, and which is turned on byunplugging of the appliance. The oscillator energizes a remote alarmcircuit, suitably located in the managers ofce, and suitable steps maybe taken to bar theft of the television set or other appiiance.

The signals from the warning box may be transmitted through the powerwiring for the motel, or may b radiated through the air. I

An important advantage of the proposed system is the low installationcost. The warning boxes or units may be plugged directly into the walloutlets, so that expensive custom electrical or custom cabinetinstallations are avoided. p

Other objects, features and advantages of the invention will becomeapparent from a consideration of the following detailed description andfrom the drawings in which:

FIG. l is a diagrammatic view of motel indicating the use of the theftprevention system of the invention;

FIGS. 2, 2a and 2b show the mechanical arrangement of a theft preventionsignal generator unit or box;

FIG. 3 is a typical circuit which may be employed ICC to produce awarning signal when the present warning system is energized;

FIG. 4 shows a typical receiver for responding to signals from the theftindication signals; and

FIG. 5 indicates an alternative arrangement for preventing removal ofthe alarm signal generator unit from a wall socket while the appliancesare plugged into the unit.

Referring more particularly to the drawings, three rooms 12, 14, 16 ofthe motel 18 are shown, in addition to the oice 20. In the motel rooms12, 14, 16, television sets 22, 24, 26 are located, and they arenormally plugged in to respective alarm signal generator boxes 28, 30,and 32. These warning boxes or units are plugged into conventional walloutlet boxes which are in turn connected to the power lines 34.

In the ollice 26, a radio receiver 36 is provided with alarm lightswhich are selectively responsive to signals from the particular alarmsignal generator boxes 28, 30 and 32, as discussed below. Signals fromboxes 28, 30 and 32 are either radiated through space to be picked up byantenna 38, or are transmitted. over power lines 34 and the input powerlines which are capacitively coupled to the input stages of radio 36.

As indicated in FIG. 1, the plug from television set 22 has been removedfrom box 28. Upon removal of the plug, the alarm circuitry in box 28 isenergized, and the signal is picked up by receiver 36. An audio tone maythen be heard at the output of .receiver 36 and a light 42 isilluminated. Suitable arrangements such as afset of tuned circuitsmatched with the warning signal transmitters in boxes 28, 3) and 32 areemployed to selectively energize the lights in the receiver 36.

FIG. 2, together with details 2a and 2b show an illustrativeimplementation of the boxes 28, 30 and 32 of FIG. l. In FIG. 2, thealarm transmission box 28 is provided with two plug prongs 52 forinsertion into a standard wall socket 54. As indicated in the detailedview of FIG. 2b, the prongs 52 are provided with points 56 which preventeasy removal of the unit 28. Removal of the plug-in unit 28 may also beprevented by the alternative shown in FIG. 5 of the drawings.

In the illustrative embodiment of FIG. 2, the alarm circuitry is mountedon the insulating printed circuit board 58. Electrical Contact to theboard 58 is made at terminals 6l) and 62 which match spring contacts 64and 66 in unit 28. When television plug 70 is plugged all the way in,its two prongs 72 and 74 engage the contacts 76 and 78, respectively.Spring contact 76 is flexible, and is biased to engage the contact 80 asbest shown in FIG. 2a, when contact 76 is not depressed by prong 72 ofthe television plug 7l);

Contact arm 80 is connected to spring contact 66 by lead S2;accordingly, when plug 70 is removed, current is applied, over one prong56, lead 841, contacts 76 and 80, lead 32 through contacts 66 and 62, tothe circuit board 58. This completes the circuit to the alarm circuit,as the'other Contact 60 is connected to the other side of thealternating current through contact 64 and the other prong S2 of theunit 28.

The operation of the warning circuitry, once it is energized, will nowbe considered in connection with FIGS. 3 and 4 of the drawings.

The circuit of FIG. 3 is made up of three principal parts, the powersupply 92, the audio oscillator 94 and the radio frequency oscillator96. These circuits are mounted on the board 58 of FIG. 2, and areenergized when power is supplied to terminals 60 and 62.

The circuits of FIG. 3 may be of any suitable form, and may `be of knownconfiguration. As implemented in the present instance, however, thepower supply 92 includes a fuse 9S, a filament transformer 100, a fullwave rectifier bridge 102, and a filter circuit having capacitor 104,resistor 106 and Zener diode 108 as component parts.

The audio oscillator circuit 94 includes the PNP transistor 110, asuitable 40-300 microhenry oscillator coil 112, resistor 114 andpotentiometer 116. With power supply and feedback circuits as shown inFIG. 3, audio frequencies of a few hundred to a few thousand cycles persecond may be obtained.

The RF oscillator employs a PNP transistor 118 and has stabilizedvoltage from the Zener diode 108 applied to the transistor collector.The frequency of the RF oscillator is determined by coil 120 andcapacitors 122 and 124. Resistor 126 is in the emitter circuit and isconnected to the junction between capacitors 122 and 124 to providesuitable feedback and emitter bias conditions. Base-to-emitter forwardbiasing current is provided through resistor 128. Audio modulation ofthe RF oscillator is accomplished by the application of signals fromaudio oscillator 94 by the network including coupling capacitor 128,resistor 130 and capacitor 132. Modulated RF signals are applied to thepower lines or to an antenna of loop type, for example, by capacitor134.

In the circuit of FIG. 4, the diode 140 represents the detector of 4aradio receiver. The radio receiver is tuned to the RF frequency of theunits 28, 30, and 32, which are all tuned to the same RF frequency, butto different audio frequencies. It is, of course, also possible to tunethe RF frequency oscillator in each of the units to the intermediatefrequency of the radio receiver and to couple from the power lines orantenna directly to the first LF. stage of the receiver.

Detected signals are coupled through transformer 142 t tuned circuits144, 146, 148, 150 and so forth. These tuned circuits .are connected inparallel, and they are, in turn, connected in series with the speaker152. When one of the units, such as unit 28 is energized by the removalof a plug, the corresponding tuned circuit 144 is energized, and light42 in tuned circuit 144 is energized. In addition, a warning audiosignal of the frequency of the tuned circuit may be heard fromloudspeaker 152.

FIG. shows an alternate arrangement for securing the warning units inposition which provides greater flexibility than the use of detents 56on the prongs of the warning units as shown in FIG. 2. In the units ofFIG. 5, the electronics of the warning unit 162 is not shown. Forinstallation, the screw or bolt 164 is removed from the center of aconventional receptacle cover plate 166, the prongs 168 and 170 of theunit 162 are plugged in through the cover plate 166. The unit 162 isthen secured in place by inserting the screw 164 into a recess 172 inthe unit 162 through a small opening through the rear wall of the unit162, and into its original threads behind the cover plate 166.

Following securing of the unit 162 in place, the recess 172 is closed bya cover plate 174 which contains openings to receiver appliance plugs 70and 701 which may be arranged to energize the warning circuitry in muchthe same manner as described above in connection with FIG. 2 of thedrawings. Obvious minor modifications would of course be necessary toadapt the physical and electrical arrangements of FIGS. 1 through 4 tothe modified physical structure shown in FIG. 5. Thus, the electricalcircuitry could be divided into portions above and below the recess 172,and either one or both of the plugs 70 and 701 could be arranged toenergize the Warning circuitry when removed. The advantage of the styleof FIG. 5 is that it can be more readily removed and used in a differentwall socket when such a change appears to be necessary or desirable.

In closing, it is again noted that an important advantage of the presentinvention resides in the ease of installation. Because of the unitizedconstruction, no electricians or carpenters are required for specialwiring or installation.

It 1s to be understood that the above-described arrangements areillustrative of the principle@ Qf the invention. Numerous otherarrangements may be devised by those skilled in the art. Thus by way ofexample and not of limitation, a simple but very noisy buzzer may beinstalled in the alarm units. When the appliance plug is pulled out, theunit will set up such a racket that the would-be thief will probablyplug the appliance back in. Otherwise, the manager or one of the motelemployees will soon hear the audio alarm signal.

What is claimed is:

1. In combination:

an alarm circuit;

a power receptacle including a switch 'which is changed in its state bythe prongs of a plug as they are inserted into and removed from thereceptacle;

means connected to said switch for energizing said alarm circuit as theplug is removed from said receptacle; and

a small box assembly having electric plug prongs extending directly fromits side to plug into a standard .wall socket, containing said alarmcircuit, said power receptacle and switch, said box assembly furtherincluding means for preventing removal of said box assembly from saidstandard wall socket following mounting the box assembly into the wallsocket and plugging an appliance into the power receptacle on the box.

2. A unitized alarm system for preventing the theft of appliances frommotel rooms or the like comprising:

a plurality of box like alarm units each having protruding prongs fordirectly plugging into standard service outlets in respectivelydifferent rooms, each of said units having at least one socket forreceiving an appliance plug, electronic circuit means within each unitfor giving a unique alarm signal when an appliance plug is removed froma unit, and means for preventing removal of the units from the serviceoutlet following plugging of the units into the outlet and theappliances into the units; and

receiver means responsive to the alarm signal to provide a uniquewarning signal, corresponding to the unique alarm signal.

3. A plug-in alarm apparatus comprising:

an alarm box;

a pair of prongs extending directly from said box for engagement with apower line receptacle;

an alarm circuit in the box;

a receptacle on the alarm box for receiving an appliance plug;

means for preventing removal of the alarm box from the power linereceptacle; and

switch means for energizing the alarm circuit when the appliance plug isremoved from the receptacle on the alarm box regardless of the state ofenergization of the appliance.

References Cited UNITED STATES PATENTS 3,229,300 l/l966 Thompson et al.340`3l0 X 3,411,150 11/1968 Shulein 340-216 2,562,069 7/ 1951 Stein etal.

2,681,443 6/1954 Caulk.

2,979,706 4/1961i Simon et al 340-224 3,045,226 7/ 1962 Trayner 340-2803,127,597 3/1964 Lewin et al. 340-280 3,247,502 4/ 1966 Eberts 340-224 X3,274,578 9/1966 Block et al. 340-310 X 3,289,194 11/1966 King 340-280JOHN W. CALDWELL, Primary Examiner D. L. TRAFTON, Assistant Examiner US.Cl. XR. 340-224, 216

